use

If you have more than one event-model specified at the ./configure script, then you can tell nginx which one do you want to use. By default nginx looks for the most suitable method for your OS at ./configure time.

You can see the available event-models and how you can activate it at the ./configure state here

worker_connections

Syntax:worker_connections number

Default:

The worker_connections and worker_processes from the main section allows you to calculate max clients you can handle:

max clients = worker_processes * worker_connections

In a reverse proxy situation, max clients becomes

max clients = worker_processes * worker_connections/4

Since a browser opens 2 connections by default to a server and nginx uses the fds (file descriptors) from the same pool to connect to the upstream backend